Hi!
The GoogleVR plugin shipped with UE4 is deprecated since UE4.24 and the last version supporting iOS was for UE4.21. In the mean time, Google abandoned the old SDK (the one used by the GoogleVR plugin) and started developing a new SDK for Cardboard (without any support for UE4).
But, if still interested in developing for Google Cardboard, we released a plugin (Cardboard VR) that integrates the new Google Cardboard SDK in UE4, for both iOS and Android: https://www.unrealengine.com/marketplace/cardboard-vr .